The invention relates to a device and method for continuous printing of organic light-emitting diodes (OLEDs).
Organic light-emitting diodes (OLEDs), based on organic material such as polymers and/or “small molecules” as the principal material of the functional layers, have developed very rapidly in recent years. Improved efficiency, a large number of new colors, and lower usage voltages make them of interest for many areas of application. Typical applications can be low-information-content passive-matrix displays with a few thousand pixels and an icon bar, backlights for LCDs, or planar illumination elements. The advantages of OLEDs, such as Lambert's reradiation and minimal thickness, are useful for these applications.
At present, the functional layers of which an OLED consists (e.g., poly(1,4-phenylene vinylene), PPV or polyfluorene, and/or derivatives of these materials) are usually applied to the glass or film substrate and/or to a bottom and/or structured layer using the spin-on application method. This method has a number of drawbacks: the bulk of the polymer solution (about 98%) is irretrievably lost, the spin-on application process is relatively lengthy (about 30-60 seconds) and, in the case of larger substrates, it is almost impossible to apply homogeneous functional layers.
For these reasons, alternative methods of applying organic material onto large surfaces are being sought. A number of printing processes are suitable for this purpose: screen printing, pad printing, inkjet printing, letterpress and rotogravure methods [e.g., D. A. Pardo, G. E. Jabbour, and N. Peyghambrian, “Application of Screen Printing in the Fabrication of Organic Light-Emitting Devices”; Adv. Mat., 2000, 17, p. 1249-1252; K. Mori et al., “Organic Light-Emitting Devices Patterned by Screen-Printing”; Jpn. J. Appl. Phys., 2000, 39, p. 942-944; Birnstock et al., “Screen-printed passive matrix displays based on light-emitting polymers”; Appl. Phys. Lett., Vol. 78, No. 24, 2001]. These printing methods are also advantageous because they permit the organic material to be applied after it has already been structured, making multichrome or full-color OLEDs possible.
Where a majority of the processes have thus far been developed for glass substrates, flexible substrates (e.g., films) will become increasingly important in the future.
The goal of the invention is to provide a device and method for the continuous application of soluble organic material, especially polymers, to substrate, especially flexible substrates, which operate continuously.
For economic reasons, the substrates should no longer be printed using a “stop-and-go” method, as is the case with classic printing on glass substrate, but instead should be coated in a continuous process using strip material, such as material “on a roll.” In this process, the film substrate 10, which maybe pre-structured, is supplied on a roll 20 and is imprinted with one or more polymers as the film 10 is unwound from the roll 20 in a uniform motion.
The invention solves the problem in that a special screen printing method is used to print the OLEDs.
The subject matter of the invention is a device 100 for the continuous imprinting of a substrate-strip material 10 by means of screen printing, comprising at least one printing screen 5 and in which the substrate strip material 10 is supplied on a roll 20, wherein a device 30 for moving the printing screen 5 is provided which ensures that it can accompany the strip material 10 during printing and, following printing, be returned to its original position.
Another subject matter of the invention is a method for imprinting a substrate strip material 10 by means of screen printing, in which the substrate is moved past at least one screen 5, wherein the screen 5 accompanies the strip material 10 during printing.
Finally, a subject matter of the invention is a product such as an OLED, which comprises at least one functional layer 40 that was applied in a continuous process by means of screen printing.